American had previously hoped to have the jets fly again by December 3

American Airlines on Wednesday pushed back the return of its Boeing 737 MAX jets until January 2020, again reshuffling its schedule due to a grounding following two deadly crashes.

The US carrier now plans for the MAX to resume flights on January 16, 2020. The previous plan had been to bring the planes back into service on December 3.

The top-selling Boeing has been grounded since mid-March following crashes of Lion Air and Ethiopian Airlines planes that killed 346 people.

"American Airlines anticipates that the impending software updates to the Boeing 737 MAX will lead to recertification of the aircraft later this year and resumption of commercial service in January 2020," the company said.

"We are in continuous contact with the Federal Aviation Administration and the Department of Transportation."

Boeing is targeting regulatory approval for the planes' return to service this year following upgrades but the aerospace giant has noted government authorities will have the final say.

The FAA has signaled the return of the plane could occur in stages by country in light of a lack of consensus among regulators.